Supramolecular strategies to construct biocompatible and photoswitchable fluorescent assemblies

We designed and synthesized an amphiphilic copolymer with pendant hydrophobic decyl and hydrophilic poly(ethylene glycol) chains along a common poly(methacrylate) backbone. This macromolecular construct captures hydrophobic boron dipyrromethene fluorophores and hydrophobic spiropyran photochromes and transfers mixtures of both components in aqueous environments. Within the resulting hydrophilic supramolecular assemblies, the spiropyran components retain their photochemical properties and switch reversibly to the corresponding merocyanine isomers upon ultraviolet illumination. Their photoinduced transformations activate intermolecular electron and energy transfer pathways, which culminate in the quenching of the boron dipyrromethene fluorescence. As a result, the emission intensity of these supramolecular constructs can be modulated in aqueous environments under optical control. Furthermore, the macromolecular envelope around the fluorescent and photochromic components can cross the membrane of Chinese hamster ovarian cells and transport its cargo unaffected into the cytosol. Indeed, the fluorescence of these supramolecular constructs can be modulated also intracellularly by operating the photochromic component with optical inputs. In addition, cytotoxicity tests demonstrate that these supramolecular assemblies and the illumination conditions required for their operation have essentially no influence on cell viability. Thus, supramolecular events can be invoked to construct fluorescent and photoswitchable systems from separate components, while imposing aqueous solubility and biocompatibility on the resulting assemblies. In principle, this simple protocol can evolve into a general strategy to deliver and operate intracellularly functional molecular components under optical control.     

Influence of CH3 substituents on tetrahydropyrimidin-2-ylidene: σ-donating properties and in situ catalytic activities of precursor salts/Pd(OAc)2 system for C-C coupling reactions

In this study, symmetrical and non-symmetrical 1,3-dialkyltetrahydropyrimidinium salts (1·HCl and 2·HBr, respectively), bearing two methyl groups at C₅ position of the pyrimidine ring were synthesized and characterized. One of the new salts 1,3-bis(2,4,6-trimethylbenzyl)-5,5-dimethyl-3,4,5,6-tetrahydropyrimidinium tetrafluoroborate (1a·HBF₄, 1a = 6-Bn∗-Me₂) was converted to cis-[RhCl(6-Bn∗-Me₂)(CO)₂] to determine the σ-donating properties in comparison to those of their 5-membered NHC complexes. Furthermore, the in situ catalytic activities of all salts, in combination with Pd(OAc)₂, were tested for the Heck-Mizoraki and Suzuki-Miyaura type C-C coupling reactions. In contrast to the expectation, only the substituents on N,N′-atoms were found to play an important role in the catalytic activity.     

Coefficient bounds for a subclass of starlike functions of complex order

In the present work, we determine coefficient bounds for functions in certain subclass of starlike functions of complex order b, which are introduced here by means of a multiplier differential operator. Several corollaries and consequences of the main results are also considered.     

Electrical spin injection from an organic-based ferrimagnet in a hybrid organic-inorganic heterostructure

We report the successful extraction of spin-polarized current from the organic-based room temperature ferrimagnetic semiconductor V[TCNE](x) (x～2, TCNE: tetracyanoethylene; T(C)～400 K, E(G)～0.5 eV, σ(300?K)～10(-2) S/cm) and its subsequent injection into a GaAs/AlGaAs light-emitting diode. The spin current tracks the magnetization of V[TCNE](x～2), is weakly temperature dependent, and exhibits heavy-hole-light-hole asymmetry. This result has implications for room temperature spintronics and the use of inorganic materials to probe spin physics in organic and molecular systems.     

Realization of affine type A Kirillov–Reshetikhin crystals via polytopes

On the polytope defined by Feigin, Fourier and Littelmann, associated to any highest weight corresponding to a rectangular partition, we define a crystal structure of type $A_n$. We show that this crystal is isomorphic to the one obtained from Kashiwara?s crystal bases theory. Further we define on this polytope a bijective map and show that this map satisfies the properties of a weak promotion operator. This implies in particular that we provide an explicit realization of Kirillov–Reshetikhin crystals for the affine type $A_n^{(1)}$ via polytopes.     

Influence of molecular weight on the short‐channel effect in polymer‐based field‐effect transistors

In this study, we demonstrate how the intrinsic properties of a polymer can influence the electrical characteristics of organic field‐effect transistors (OFETs). OFETs fabricated with three batches of poly[2‐methoxy,5‐(3′,7′‐dimethyl‐octyloxy)]‐p‐phenylene vinylene (MDMO‐PPV) were investigated. The properties of the polymers were initially investigated using Fourier transform infrared spectroscopy (FTIR), impedance spectroscopy (IS), gel permeation chromotography (GPC), and cyclic voltammetry (CV), respectively. The structure and purity of the polymer batches were found to be very comparable, but the molecular weight (M_n and M_w) and polydispersity (PDI = M_w/M_n), varied between the samples and the HOMO and LUMO levels of the polymers were found to depend on the molecular weight properties. OFETs were then fabricated with the polymers and electrically characterized. It was observed that the channel current and the field‐effect mobility increase with increasing polymer molecular weight. The output characteristics of the transistors, on the other hand, were found to depend on the PDI of the polymer. Saturation of the channel current occurs at higher source–drain voltages and short‐channel behavior was observed to start at longer channel lengths for polymers with a higher PDI. This behavior is observed to be thickness dependent, and the short‐channel behavior was more pronounced for thicker MDMO‐PPV films. These results are explained in terms of influences of chain packing and ordering and high bulk currents on the FET output and transistor parameters. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 117–124, 2012     

Traffic aware cell selection algorithm for Tetra Trunk based professional mobile radio

Telecommunication Systems -